The background of this invention lies within the streaming cartridge tape art wherein information can be recorded at a density of eight thousand bits per inch. The tape drive incorporates a micro-computer which controls various drive functions and interfaces with a host system.
The streaming cartridge is particularly useful by virtue of the fact that in conventional tape systems, the recorded data is blocked and can be individually accessed and updated. To preserve the individuality of each record, the tape system must start and stop between records.
The foregoing requirement necessitates the incorporation of fairly long inter-record gaps. The length of the gaps is such that a conventional tape might only use approximately twenty percent of the magnetic media. This, of course, is a substantial detriment, inasmuch as the recordation and utilization of the tape is quite inefficient.
A streaming tape format can be approximately ninety seven percent efficient, due to the fact that the tape is not started and stopped over an extended period of time. The reason for this is that the typical start and stop format of a regular tape drive provides for certain interblock gaps, and data fields that are interspersed between the interblock gaps. In addition thereto, the address and the synchronous requirements are much less with regard to the streaming format.
In effect, the streaming tape system provides maximum tape utilization at a high throughput rate for those applications that do not require tape systems that access and update individual records.
Streaming tape systems, as do many other tape systems, use a read after write technique to verify the recorded data shortly after it is written. In the conventional tape system when a read after write error is detected, the tape is stopped, backed up, and rewritten. Forward creep, a feature of most conventional tape systems causes the rewritten record to be displaced in the forward direction from the previous position of the record. This, therefore, causes the inner record of the gap to be lengthened by each successive application of backups.
In a streaming system, the particular block in error is simply rewritten until no read after write errors are detected. Therefoe, short block lengths provide better tape utilization than long block lengths for streaming systems.
The streaming system can utilize a serpentine recording technique wherein the first pass is over a write and read head along a first or zero channel or track. The second track is obtained by reversing the tape direction and reading or writing with a second channel of the head, with the head body and tape in the initial relative position. On the return, the head, or in some cases the tape itself, can be moved to provide for a passage of the third or fourth tracks or channels in the same manner as the first and second.
Regardless of the foregoing, the movement of the head body relative to the tape is a necessary requirement in order to record and read various tracks or channels of the tape. To do this, in the prior art, it was oftentimes necessary to use a number of various difficult and complex methods to prevent the tearing of the tape.
The invention herein eliminates the complex methods of the prior art and incorporates a unique method and apparatus for moving the head across the tape without degradation, oxide deterioration, and in the worst case, tearing or wrinkling of the tape.
This is accomplished by maintaining an air gap, an air cushion, or an air bearing over the surface of the head as it is moved across the tape.
To do this, the head is moved laterally while the tape is moving at the beginning or toward the end of the tape when no information is to be written or read. In the alternative, when the tape is stopped, at the end of the tape, beginning of the tape, or possibly at the middle of the tape, the capstan or drive is oscillated by pulsing the motor backwardly and forwardly to provide an air cushion between the tape and the head to prevent the lateral drag of the head as it moves across the tape.
Regardless of whether the tape is a streaming cartridge tape, a cartridge using the start-stop format, or a one half inch, one inch, or any size type of tape or paper tape, the invention effectively provides for smooth transitional movement of the head across the tape through the air cushion technique of this invention.
As will be seen in the subsequent description of the preferred embodiments and the claims attendant therewith, this invention is a substantial step over the prior art in allowing tape cartridges to be utilized and used with heads that move laterally across the face thereof. The invention applies equally well to any other form of tape drive or similar mechanism where a read/write head or equivalent must be moved across the surface of the tape.